In the manufacture of semiconductor devices, a plurality of integrated circuits are simultaneously prepared in a semiconductor wafer through the use of conventional photolithographic techniques. Thus, for example, a wafer may contain up to 1000 or more separaate integrated circuit which have been formed on the substantially planar surface area of the wafer according to conventional techniques in the art as, for example, by diffusing or otherwise forming predetermined patterns in a silicon body. It is also convenient to provide a plurality of secondary devices such as contact pads, test monitor devices, devices for measurement and alignment, etc. on the planar surface adjacent the outer perimeter of each integrated circuit or other semiconductor device. Each single integrated circuit is of relatively minute dimensions so that it is convenient to simultaneously form a plurality in a single wafer while marking the boundaries between the individual devices by scoring along perpendicular axes referred to as scribe lanes or streets.
In accordance with techniques well known in the art, after a semiconductor wafer has been formed into interconnected semiconductor devices. The chips are tested to identify those which contain properly functioning properties and are satisfactory and those improperly formed or malfunctioning and unsatisfactory. As mentioned earlier, it is common practice to put test, measurement, alignment and die seal structures in the scribing lanes. After testing, adjacent satisfactory chips are left joined together while unsatisfactory chips are separated or the entire wafer is separated and the unsatisfactory chips are discarded. Separation (or dicing) may be performed by conventional techniques such as sawing or laser cutting along the scribe lane.
The scribing step itself, while relatively simple, is not free of problems. For example, the wafer contains a substantial amount of metallization in the area of the scribe lanes which, when sawed or separated often leaves relatively large jagged pieces of metal commonly referred to as shards or slivers that remain attached to the edge or edges of the semiconductor device. Such shards of metal often turn or bend over the scribe lane or break off interfering with the intended properties of the devices, for example by contacting bonding wire or other wires in the device. Such contact often results in an unsatisfactory, malfunctioning device that must be discarded resulting in a lowered yield of semiconductor devices from the manufacturing process.
One of the greatest problems of large scale integration of, for example, electronic circuits, is that of obtaining a high enough yield on each wafer of circuits to be commercially profitable. As the number of devices per circuit increases, the yield often decreases proportionally. It is therefore highly desirable to minimize the number of devices that must be discarded as unsatisfactory. Moreover, because the scribing process may itself produce unsatisfactory devices, improvements in this step are of increasing importance.
In Japanese Patent Application Publication (Kokai) No. 56-43,740, there is described a method for providing a semiconductor wafer with metal coating in the scribing area which can be scribed with a reduced risk of bending of the metal film by providing at the scribe lane a metal coating having a strip-like configuration and a row of slits arranged along the center lines of the metal film and oriented perpendicularly to the center lines. According to the Kokai, it is possible to protect the wafer from deterioration of properties by the use of such slits in the scribe areas since, if portions of metal film are bent during the scribing operation, the dimensions of the bent portions are limited to the spaces between adjacent slits with the maximum length being equal to the length of the slits so that in case of bending, the bent portion cannot come into contact with bonding wires or pattern elements.
Such a construction, while fine for certain applications, would not qualify the semiconductor devices produced for certain other applications, such as, for example certain applications which require that the device conform to military standards, wherein the dimensions of any metal or metal shards present on the device must meet certain minimum size standards. For example, certain U.S. government specifications require that in such devices, metal shards or turnover may not exceed 0.4 mil (10 microns) in any given dimension. The devices of the Japanese Kokai, however, produce shards that are generally 2 to 5 mils (50 to 200 microns) rendering such devices unusable for such applications and rejectable as unsatisfactory.
Additionally, in the device described in the Japanese Kokai, great precision in performing the sawing or separation is required and there is little tolerance for variation in the scribe operation. Moreover, as illustrated in the drawing of the publication, metal shard formation appears to be of concern only in the corners of the devices, the slits appearing to be present in the corners only.
An object of this invention is the provision of a simple method for increasing the yield of satisfactory semiconductor devices in semiconductor wafers.
Another object of the invention is the provision of a semiconductor wafer which may be variably and flexibly scribed and tested.
Another object of the invention is the provision of a semiconductor device comprising a metal film which may be scribed along multiple scribe lanes without producing metal shards or bent portions that exceed 0.4 mils (or 10 microns) in any dimension.
Another object of the invention is to provide a method of scribing semiconductor wafers in which the dimensions of metal shards or bends resulting from the scribing are controllable, predetermined and pre-designed.
There and other objects of the invention will be apparent from the description of the invention which follows.